Melanoma is the most rapidly progressing malignancy in the United States, accounting for 75% of all skin cancer-associated deaths. Lucas, R. et al., “Global Burden of Disease of Solar Ultraviolet Radiation”, Environmental Burden of Disease Series, No. 13, News Release, World Health Organization, 2006. Currently, a dielectric barrier discharge (DBD) device is being tested for the treatment of melanoma. DBD requires that the target tissue be placed between two metal plates that are used as typical type electrodes. Gregory, F. et al., “Floating Electrode Dielectric Barrier Discharge Plasma in Air Promoting Apoptotic Behavior in Melanoma Skin Cancer Cell Lines”, Plasma Chemistry & Plasma Processing, Volume 27, Issue 2, pp 163-76, April 2007; Sensenig, R., et al., “Non-thermal Plasma Induces Apoptosis in Melanoma Cells via Production of Intracellular Reactive Oxygen Species”, Annals of Biomedical Engineering, Volume 39, Issue 2, pp 674-87, February 2011. Multiple rapid pulses of DBD plasma therapy can cause electro-deformation of cells, which opens pores and disrupts cellular membranes. Nuccitelli, R., et al., “Nanosecond Pulsed Electric Fields Cause Melanomas to Self-destruct”, Biochem. and Biophys. Res. Commun. 343, pp 351-360, 2006; Qin, H., et al., “Molecular Dynamics Analysis of High Electric Pulse Effects on Bilayer Membranes Containing DPPS and DPPS”, Plasma Science, IEEE Transactions, Volume 34, Issue 4, pp 1405-11, 2006. Although surgical incision is still the best way to remove primary melanoma, there is still a need to target cells that escape surgical resection.
In recent years, atmospheric pressure non-thermal plasmas have been used in various medical applications. Laroussi, M., “The Biomedical Applications of Plasma: A Brief History of the Development of a New Field of Research”, Plasma Science, IEEE Transactions, Volume 36, pp 1612-4, 2008. Since non-thermal plasmas do not give off heat they can be therapeutic. Non-thermal plasmas are non-toxic, and can promote sterilization.
Currently, non-thermal plasma is being investigated for its potential role in wound healing, tissue incision, protein destruction, cell and tissue modification, bacterial inactivation as well as cancer treatment. See, respectively, Fridman, G., et al., “Blood Coagulation and Living Tissue Sterilization by Floating-Electrode Dielectric Barrier Discharge in Air”, Plasma Chemistry & Plasma Processing, Volume 26, Issue 4, pp 425-42, August 2006; Vankov, A. et al., “Nanosecond Plasma-mediated Electrosurgery with Elongated Electrodes”, Journal of Applied Physics, Volume 101, pp 124701-7, 2007; Stoffels, E., et al., “Cold Atmospheric Plasma: Charged Species and Their Interactions with Cells and Tissues”, Plasma Science, IEEE Transactions, Volume 36, Issue 4, pp 1441-57, 2008; Gaunt, L. F., et al., “Bactericidal Action of the Reactive Species Produced by Gas-Discharge Nonthermal Plasma at Atmospheric Pressure: A Review”, Plasma Science, IEEE Transactions, Volume 34, Issue 4, pp 1257-69, 2006; Kim, G. C., et al., “Air Plasma Coupled with Antibody-conjugated Nanoparticles: A New Weapon Against Cancer”, J. Phys. D: Appl. Phys., Volume 42, pp 032005-10, 2008; and Esser, A. T., et al., “Towards Solid Tumor Treatment by Nanosecond Pulsed Electric Fields”, Technol. Cancer Res. Treat., Volume 8, Number 4, pp 289-306, August 2009.
Non-thermal plasma is an ionized gas with electron densities of 1011-1014 [1/cm3] and typical energies of 1-5 [eV]. Despite its high energy, non-thermal plasma exhibits near room temperature characteristics due to the low number density of electrons. Thus, non-thermal plasma is suitable for biological applications such as cell and tissue processing.
A plasma torch is a good source of reactive species, which have been shown to induce apoptosis due to the energetic electrons. Klaunig, J. E., et al., “The Role of Oxidative Stress in Carcinogenesis”, Annual Rev. Pharmacol. and Toxicol., Volume 44, pp 239-67, February 2004. Recent studies have shown that non-thermal plasma can induce apoptosis to a limited extent. Gregory, F. et al., “Floating Electrode Dielectric Barrier Discharge Plasma in Air Promoting Apoptotic Behavior in Melanoma Skin Cancer Cell Lines”, Plasma Chemistry & Plasma Processing, Volume 27, Issue 2, pp 163-76, April 2007.
Tirapazamine (referred to in the art as SR-4233 or TPZ) is an investigational drug for treating cancer. At sufficiently low levels of oxygen (referred to in the art as hypoxia), commonly found in solid tumors in humans, TPZ is activated to a toxic radical, causing cell death. It is characteristic of tumor cells to be resistant to treatments of radiotherapy and many anti-cancer drugs. TPZ is a powerful cytotoxic agent that encourages programmed cell death (referred to in the art as apoptosis) by inducing disruptions in single and double stranded DNA, as well as chromosomal breaks. Additionally, TPZ causes cells to become more sensitive to other ionizing radiation and other cytotoxic agents. As such, since TPZ is activated to its toxic form preferentially in the hypoxic areas of solid tumors, the benefits of the combination of TPZ with conventional anti-cancer treatments can be realized.
The chemical structure of TPZ is a benzotriazine di-N-oxide and its chemical name is 3-Aminobenzo[e][1,2,4]triazine 1,4-dioxide. It was originally formulated in 1972 for use as an herbicide, or weedkiller, and was not used clinically until over a decade later, in 1986. Clinically, TPZ has had only been minimally effective in trials; however, it has been used as a central compound in the development of several more recent compounds that have better cancer-treating properties.
As shown below, TPZ recycles between the inactive and active states:
For example, P450 (cytochrome) oxidoreductase (otherwise known in the art as POR), 5-methyltetrahydrofolate-homocycstein methyltransferase reductase (otherwise known in the art as MTRR), and FAD-dependent oxidoreductase domain containing 2 (otherwise known in the art as FODRED2) can be suitable reductases; however, any suitable reductase known in the art is contemplated. For example, it is believed that tirapazamine produces hydroxyl and/or benzotriazinyl radicals as DNA damaging reactive species. The free radicals that are generated within the nucleus of the cell cause single- and double-stranded breaks in DNA, base damage, and cell death. Tirapazamine also inhibits topoisomerase II, an enzyme that is responsible for cutting both strands of a DNA helix simultaneously in order to manage super coils and avoid tangling of the chromosomes. The inhibition of this enzyme results in impaired ability of the cell to repair radiation-induced DNA breaks. Tirapazamine causes hypoxic cells to become more sensitive to the damaging effects of ionizing radiation. Moreover, tirapazamine can downregulate HIF-1α (or HIF1α) expression by decreasing HIF-1α protein synthesis. HIF-1α expression can indicate a cancer that is resistant to anticancer drugs, for example, topoisomerase I inhibitors. However, tirapazamine has not been used with non-thermal plasma clinically because of its toxicity.
Therefore, there is a long-felt need for a combination therapy for treating cancer. There is also a long-felt need for a combination therapy for treating cancer featuring a non-thermal plasma and a plasma torch. Additionally, there is a long-felt need for a therapy for primary and recurrent melanoma. Furthermore, there is a long-felt need for a combination therapy for treating cancer featuring a non-thermal plasma and a DNA damaging agent that promotes cell death where the DNA damaging agent is arranged to activate only under a low oxygen condition. There is also a long-felt need for a non-thermal plasma device which is versatile and effective at inducing apoptosis and/or necrosis and reactive oxygen species. Finally, there is a long-felt need for a combination therapy for treating cancer where the components of the therapy promote cell toxicity individually and in conjunction.